The polychlorinated biphenyls (PCBs) and certain chlorinated pesticides are readily taken up by the blood and its components and transported to the liver where they are readily released. Our studies suggest that these compounds are distributed between the red blood cells, albumin, and lipoproteins at ratios which vary according to the lipophilicity of the chlorinated hydrocarbon involved. Thus, the process is thought to be a passive one in which the physical and chemical properties of the chlorinated hydrocarbons determine the blood constituent in which they will be most concentrated.